By applying a conversation analytic approach to analyze the fine-grained manifestation of authority in classroom interaction, we examine the interaction between a teacher and a student while the student presented a solution at the whiteboard. This case highlights the complexity of shared authority and the ways that authority is construed by discourse practices and negotiations over the ownership of knowledge. We offer a nuanced interpretation of how the teacher and student shared epistemic authority through their joint activity. Further, we argue for the importance of distinguishing teachers' epistemic authority and deontic authority to further our understanding of how a teacher can share authority with students during instruction. [For the complete proceedings, see ED629884.]